1. Field of the Invention
The present invention relates to a mold clamping device for an injection molding machine and, more particularly, to a so-called double cylinder type mold clamping device which performs mold opening and closing and mold clamping by separate cylinders.
2. Description of the Prior Art
As already known, the applicant in the present case has previously proposed a double cylinder type mold clamping device for an injection molding machine in which a slide platen (hereinafter referred to simply as "slide") which supports a movable mold is advanced toward and retracted from a molding machine base (hereinafter referred to simply as "base") which supports a fixed mold, through generally four tie rods and mold opening/closing cylinders each of which are fixed to the base, thereby performing opening and closing of both molds and also performing mold clamping in a closed state of both molds, and in which, in order to attain a reduction in size of the cylinders and a structural simplification by eliminating the oil filling valve, an engaging portion such as a groove-like toothed face or the like is formed on the outer peripheral surface on the tie rod, and an opening/closing split mold-like locking member which is disengageably engageable with the said engaging portion is slidably mounted on the tie rod, the tie rod serving as a receiving member for mold clamping reaction, and with a mold clamping cylinder being mounted between the locking member and the slide. In the fitting structure between the slide and the tie rods on which the slide slides in such type of a mold clamping device, a long and large guide bush structure has heretofore been provided on the inner surface of the tie rod sliding bore of the slide in order to prevent knocking when the slide moves and which passes the engaging portion such as a groove-like toothed surface or a threaded groove formed on the outer peripheral surface of the tie rod. As a result, not only is the bush structure complicated and larger in size, but also the inside of the tie rod is narrower. Moreover, in the case of a utilizing a bushing, the occurrence wear is a reoccurring problem.
In such type of mold clamping device, moreover, as means for engaging the locking member with the engaging portion and locking it onto the tie rod, there has typically been adopted means for predetermining the size (thickness) of the mold used, or means for determining such on the basis of detection of the engaging portion, e.g. a groove-like toothed surface, of the tie rod by means of a detector. However, the aforementioned sizing means has the drawback that the mold size (thickness) is restricted, and the latter detector means leaves something to be desired with respect to reliability and durability because of frequent daily operations no matter whether the detection is accomplished electrically, magnetically or optically. Further, since the locking members on, say, four tie rods are each driven individually, the structure of the clamping device and that of the detector are more complicated.